Evaluation of flocculants for the recovery of freshwater microalgae

The use flocculants on the recovery of freshwater microalgae is studied. Flocculants tested include metal salts, chitosan, and polyelectrolytes used in wastewater treatment processes. Influence of flocculant, but also the doses and biomass concentrations affecting biomass recovery as well as the concentration factor has been evaluated. Results showed that the use of metal salts or chitosan was not efficient, whereas polyelectrolytes allow the efficient recovery of biomass, at doses of 2-25 mg per gram of microalgae biomass. The required doses depend on the particular polyelectrolyte and the freshwater strain present; but cationic polyelectrolytes are generally recommended. The use of polyelectrolytes does not adversely affect water reuse in the production process. The concentration factors obtained are higher than 35 in most cases. Such high concentration factors allow a reduction in the equipment size necessary for biomass dewatering, thus improving the viability of using these microorganisms in biofuel or wastewater processes.